linux-kernel - Re: [PATCH v2] watchdog: rti_wdt: Set min_hw_heartbeat

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Date: Tue, 9 Apr 2024 16:44:25 -0500
From: Judith Mendez <jm@...com>
To: Francesco Dolcini <francesco@...cini.it>
CC: Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck
	<wim@...ux-watchdog.org>,
        <linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] watchdog: rti_wdt: Set min_hw_heartbeat_ms to
 accommodate 5% safety margin

Hi Francesco,

On 4/9/24 2:52 PM, Francesco Dolcini wrote:
> On Tue, Apr 09, 2024 at 02:37:15PM -0500, Judith Mendez wrote:
>> Hi all,
>>
>> On 4/6/24 8:01 AM, Guenter Roeck wrote:
>>> On Thu, Apr 04, 2024 at 10:33:19AM -0500, Judith Mendez wrote:
>>>> On AM62x, the watchdog is pet before the valid window
>>>> is open. Fix min_hw_heartbeat and accommodate a 5% safety
>>>> margin with the exception of open window size < 10%,
>>>> which shall use <5% due to the smaller open window size.
>>
>> Please do not merge this patch, I will add an additional
>> patch removing the hack in this driver.
> 
> Is the patch buggy, or you are just talking about an additional clean-up?
> If it is an additional patch and this code is fine, why holding it back?

1. If we leave the hack, the hack shifts the valid window. This
is not desirable behavior. It is better to add a safety margin
that works in all possible scenarios.

2. 5% safety margin works in almost all cases except when the
timeout is < 5s. This due to a requirement of a min of 0.25s for the
safety margin due max possible error. At < 5s timeout, 5% is not
enough.

I am not 100% sure if using < 5s timeout is a real use-case
but I would rather use a safety margin that works for all cases.

~ Judith